1. Field of the Invention
The present invention relates to a gas tungsten arc welding process for welding steel boiler tubes and more particularly, to a flux assisted insert welding that uses a consumable insert ring to substantially increase weld penetration.
2. Brief Description of Prior Art
Steel boiler tube replacement welds are currently done manually and generally characterized by tight tolerances on the radial clearance between the tubes which present special challenges. To allow the welder access to the joint and ensure complete penetration, the tube ends are prepped with a 37 degree bevel or other special end prep geometry. Due to the volume of material removed by the bevel process, multiple weld passes are required to complete the weld. As a result, the process requires a considerable amount of material preparation time and cost. Although manual welding can achieve acceptable weld quality, a highly skilled welder is required, which only exacerbates the complexity and expense of the welding process. Gas Tungsten Arc Welding (GTAW) using a flux for increasing weld penetration is known. U.S. Pat. No. 7,285,747 discloses an insert ring design used in the joining of steel tubes by a GTAW process. The '747 insert ring is used as a filler metal and includes a pair of grooves to retain a penetration enhancing flux while transporting and positioning the insert ring. However it was found that once the flux was applied to the '747 insert ring, the flux would dry before the ring was finally positioned. Once dried the flux had a brittle or “flaky” nature, and would fall off. As a result, the flux retention aspect disclosed in '747 adds more complexity to the process, results in severe welding defects, and causes quality control issues.
To the best knowledge of the applicants, a suitable, commercially practicable method has not been found for welding in a space restricted area, such as a boiler tube replacement application, using GTAW in combination with a consumable insert ring and where the use of a flux is desired in order to provide the penetration capabilities required by the design of the joint and the material properties.
As will be seen from the subsequent description, the preferred embodiments of the present invention overcome shortcomings of the prior art.